The design and contruction of cord-type repairs presents a number of mutually conflicting criteria. Thus, it is imperative that the cord be strong enough to avoid breaking during insertion. This requirement is easy to meet because it is a simple matter to provide a cord of sufficient strength to withstand insertion, by employing a tightly twisted or a braided cord material. The problem with this, however, is that such cords do not readily conform to the random shapes of typical punctures. In addition, it is very difficult to impregnate such tightly twisted cords thoroughly enough and with sufficient elastomer to provide an impermeable repair. Experience has shown that the elastomer-to-cord ratio must be at least 180 parts by weight of elastomer to 100 parts by weight of cord (preferably over 200 parts of elastomer), and that the impregnation must reach the core of the individual yarns which comprise the cord. Also, the cord must be relatively soft and malleable so that it can yield to the contour of a cut or puncture. These requirements dictate the use of relatively loosely twisted and hence weak cords, and, of course, as these criteria are increasingly satisfied, the risk of breakage during insertion increases proportionately.
The size of the cord also imposes further restriction. Thus, while it is desireable to have a large cord with sufficient malleability to fit a wide range of puncture sizes, the larger the cord is, the more resistance it has to insertion and hence the greater is the risk of breakage.
Considerable attention has been paid in the past to the tools employed in the insertion of cord repairs. Thus, a tightly twisted cord of the right size can be strong enough to be inserted into a puncture with a simple screw driver, but, as explained above, such a tightly twisted cord does not make a good repair. When the cord is soft and malleable, however, sufficiently to yield to the contour of typical punctures, the shear forces created by insertion with a screw driver are so great that breakage generally occurs. This problem is aggravated as the cord diameter is increased. In addition, a screw driver or similar simple probe tends to pull the repair back out through the puncture, again increasingly with size. For these reasons cord-type repair tools as described in U.S. Pat. No. 3,783,715 and D-239, 430 have been employed. Such tools have a cylindrical body with an elongated eye at one end and a slit communicating between that end of the tool and the eye. The base of the eye is provided with tapered recesses on each side extending toward the shank of the tool. These recesses minimize the shear forces acting on the cord during insertion. The slit at the end of the eye is designed so that, after the cord has been inserted, the tool will draw a loop of the cord (inside the tire) back toward the puncture and, before releasing the loop through the slit, it wedges the loop against the cord in the puncture. This wedging action together with the high degree of adhesion between mutually contacting surfaces of the impregnated cord material greatly increases the resistance of the cord to extraction and thereby increases the ability of the tool to be withdrawn without simultaneously withdrawing the cord. In addition, tools of this type have the added advantage over simple probes of the screw driver type, in that the tip end of the tool leads the way into the puncture and widens the opening prior to the cord's coming into any contact with the tire. This reduces abrasion on the cord.
Although tools of the type described have permitted successful insertion of cords of an appropriate minimum size which are sufficiently malleable and weak to make adequate repairs, there has continued to be a need for a tool which will permit even weaker, more malleable cords and/or larger cords to be inserted without breakage. It is a basic object of this invention to provide such a tool.